This article argues that even if we grant that murderers may deserve death in principle, retributivists should still oppose capital punishment. The reason? Our inability to know with certainty whether or not individuals possess the necessary level of desert. In large part due to advances in science, we can only be sure that no matter how well the trial is administered or how many appeals are allowed or how many years we let elapse, we will continue to execute innocent persons for as long as we legalize capital punishment. Thus, on grounds of desert, this article argues that retributivists should oppose capital punishment.